1. Field of the Invention
The invention relates to a method for measuring a thickness of a coating of a constructional unit, in particular a heat-compatible coating on a component of a gas turbine.
2. Brief Description of the Related Art
Fluid-flow machines, in particular gas turbines, are often exposed to high temperatures during operation and are therefore provided with heat-compatible, often ceramic, coatings. These coatings are applied, for example by plasma-arc spray guns, to the metallic components in a number of layers, in that for each layer a number of strips of the layer material are sprayed onto the surface next to one another or else overlapping, until the surface is covered. The layer thickness can be measured during development of the process, for example by micrographs.
Variations during the coating process in production cannot be detected by capacitive measuring methods for metallic coatings and only to a restricted extent for ceramic coatings.
Apart from an exact determination of the layer thickness, for offline programming of the spraying device in particular, it is necessary to know an exact contour and mass-intensity distribution of the plasma/layer-material jet emitted by the spraying device. Without exact knowledge of them, the offline programming is inaccurate and the layer thicknesses, particularly at critical locations such as corners and radii, must be verified in a number of iterations by complex and cost-intensive micrographs.